In video compression systems, a source video sequence may be partitioned into successive groups of pictures or GOPs, where each picture or frame in the GOP may be of a pre-defined picture coding type. For example, in MPEG-2 applications, these picture coding types may comprise intra-coded pictures, predicted pictures, and bidirectional-predicted pictures. The intra-coded or “I” pictures may only use the information within the picture to perform video compression. These self-contained “I” pictures provide a base value or anchor that is an estimate of the value of succeeding pictures. Each GOP may generally start with a self-contained “I” picture as the reference or anchor frame from which the other frames in the group may be generated for display. A GOP may start with an “I” picture when describing the transmission, decoding, and/or processing order of a picture sequence, for example. A GOP may start with bidirectional-predicted pictures when describing the display order of a picture sequence, for example. The GOP frequency, and correspondingly the frequency or periodicity of “I” pictures, may be driven by specific application spaces. The predicted or “P” pictures may use a motion estimation scheme that generates motion vectors that may be utilized to predict picture elements from previously encoded pictures. Compressing the difference between predicted samples and the source value results in better coding efficiency than that which may be achieved by transmitting the encoded version of the source picture information. At a receiver or decoder side, the compressed difference picture is decoded and subsequently added to a predicted picture for display.
The bidirectional-predicted pictures or “B” pictures may use multiple pictures that occur in a future location in the GOP and/or in a past location in the GOP to predict the image samples. As with “P” frames, motion estimation may be used for pixel prediction in “B” pictures and the difference between the original source and the predicted pictures may be compressed. At the receiver or decoder end, one or more “B” pictures may be motion compensated and may be added to the decoded version of the compressed difference signal for display. Since both the “P” pictures and “B” pictures may be based on other pictures, they may be referred to as inter-coded pictures.
In the H.264 video standard, for example, pictures may be referred to as reference and non-reference pictures. The reference pictures may correspond to pictures that may be utilized to predict other pictures in a picture sequence, while the non-reference pictures may correspond to pictures that may be predicted from other reference pictures in a picture sequence. In this regard, the “I” pictures, “P” pictures, and/or “B” pictures may correspond to H.264 reference pictures, while only the “P” pictures, and/or “B” pictures may correspond to H.264 non-reference pictures, for example.
When the “I” picture in a GOP structure samples, for example, textured areas that are moving in a very consistent way, coding artifacts may be introduced and/or propagated to the remaining pictures in the GOP from the encoding of the “I” picture. The visible inconsistencies that arise at the boundary between a current GOP and a next GOP as a result of the artifacts introduced by the encoding of “I” pictures are known as “I picture clicking,” “I picture popping,” or “I frame clicking.” Such visible artifacts are generally detrimental to video quality and are of particular concern in display applications where “I” pictures are utilized for accessing the video sequence and/or utilized as an anchor for additional video signal processing operations.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.